In a recent
letter to the editor “Ventilatory modes. What’s in a name?”[1] Authors provide
a strong argument for the need to standardize terminology in regards to
mechanical ventilation and propose an oversimplified classification system
specifically for non-invasive ventilatory devices. I applaud the authors for
their call to action; conversely their viewpoint is neither novel nor
applicable to ventilator taxonomy.
For greater
than two decades, Robert Chatburn has invested tremendously in the creation, refinement,
education, promotion, and defense of a standardized taxonomy for mechanical
ventilation [2-9]. Chatburn’s current
classification system [1, 10] addresses the concerns that Dr. Rabec and
colleagues present, which can be easily applied to non-invasive ventilation
(NIV). Establishing a new oversimplified classification system specifically for
NIV, I believe would further exacerbate the confusion.
The
classification system proposed by Rabec et al reduces to three over-simplified
characteristics (control variable, trigger variable, and cycle variable). These
are necessary, but not sufficient, characteristics from which to construct a
useful classification system. Attempting to use them to sort out modes
ultimately frustrates the device operator.
I have three
main arguments why such over-simplification does not work in regards to
mechanical ventilation terminology.
First, Complexity has already been engineered into
the product/device.
The level of
sophistication of ventilator mode taxonomy is dependent on the intricacy of the
device itself. For example a NIV device with “Adaptive Servo Ventilation” is
far more intricate than a “Downs Regulator” used for Continuous Positive Airway
Pressure (CPAP). Both may provide CPAP
therapy, conversely they are not equal in classification. One can merely reduce
the terminology, yet this does not change the complexity of the device and thus
leaves a gap in understanding.
Second, the additional classification schemes
foreshadow unfortunate events.
Rabec et al
justify their argument by emphasizing that there are no regulations for medical
manufactures in regards to ventilator terminology and mention that new modes of
ventilation are created with little changes to the previous mode. I believe
this does support the need for standardization, however negates their proposal
for oversimplification. Only by including the additional classification details
(eg, targeting scheme and operational algorithms) one can truly identify if a
new mode provides any benefit or is merely a marketing scheme.
Additionally,
once one is proficient utilizing the taxonomy proposed by Chatburn, the
operator can apply this knowledge to unfamiliar modes and predict ventilator
interactions to changes in pulmonary mechanics and/or changes in patient inspiratory
demand.
An example
of this can be demonstrated with the ventilator manufacture, marketing, and
operator use of a mode which has been informally referred to as “Adaptive
Pressure Control”, or APC [11]. APC has been available as a ventilator mode for
greater than twenty years. This mode is characterized by a more advanced
“adaptive targeting system” as compared to earlier “set-point” targeting
systems [8]. However, it has been marketed as “the best of both worlds” in
which the operator can target a preset tidal volume (similar to volume control
ventilation) and the patient is available to receive high inspiratory flow
rates if needed (because the within-breath control variable is pressure, not
volume).
In 2007 Jaecklin demonstrated that APC in a variety of ventilators
regularly delivered excessive tidal volume in response to sudden increases in
patient compliance or decreases in resistance potentially putting neonates at
risk for lung injury [12]. Thus deflating manufacturers advertised persuasive claims
of precise volume-targeting.
Within
recent years in the United States, anesthesia delivery system manufacturers
have made APC available on their newer generation anesthesia machines. The mode
has been highly marketed for surgical procedures in which patient positioning
or insufflation of the abdomen creates dramatic changes in pulmonary mechanics
(e.g. laparoscopic, thoroscopic, prostatectomy, and bariatric procedures).
Armed with prior knowledge of the operational algorithm of APC and knowing the issues
in regards to tidal volume consistency during dramatic changes in pulmonary
mechanics, the operator can easily predict what will happen during these
surgical procedures. The abstract “Adaptive Pressure Control: tidal volume
variance during simulated bariatric laparoscopic surgery” verified the
inconsistency in tidal volume delivery and latency of tidal volume adaptation
during inflation and deflation of pneumoperitoneum [13].
Third, oversimplification infers a notion that
anyone can operate/manage a ventilatory device.
In their
proposal, Rabec et al support their argument by stating that application of NIV
has been generalized and is carried out by non-specialized healthcare
providers. I suggest that simply reducing the complexity of ventilator terminology
may imply that the device is easy to use. The taxonomy suggested by Chatburn
divulges specific intricacies which the operator may not understand or even be
aware of. If the operator cannot apprehend these specifics related to
ventilator breath delivery, then one should not attempt to use the mode in
question. I would reinforce that mechanical ventilation should not be managed
or applied by non-specialized health care practitioners.
I too share
the goal “to make NIV management easier in clinical practice” however dumbing
down ventilator taxonomy will not contribute to this objective.
References
1.
Rabec
C, Langevin B, Rodenstein D, Perrin C, Leger P, Pepin JL, Janssens JP,
Gonzalez-Bermejo J. Ventilatory modes. What’s in a name? Respir Care 2012; 57
(12): 2138-2150.
2.
Chatburn
RL. A new system for understanding mechanical ventilators. Respir Care 1991; 36
(10): 1123-1155.
3.
Chatburn
RL. Classification of mechanical ventilators. Respir Care 1992; 37 (9):
1009-1025.
4.
Branson
RD, Chatburn RL. Technical description and classification of modes of
ventilator operation. Respir Care 1992; 37 (9): 1026-1044.
5.
Chatburn
RL, Primiano FP Jr. A new system for understanding modes of mechanical
ventilation. Respir Care 2001; 46 (6): 604-621.
6.
Chatburn
RL. Computer control of mechanical ventilation. Respir Care 2004; 49 (5):
507-517.
7.
Chatburn
RL. Classification of ventilator modes: Update and Proposal for Implementation.
Respir Care 2007; 52 (3): 301-323.
8.
Chatburn
RL, Mireles-Cabodevila E. Closed-loop control of mechanical Ventilation:
description and classification of targeting schemes. Respir Care 2011; 56 (1):
85-102.
9.
Chatburn
RL, Volsko TA, Hazy J, Harris LN, Sanders S. Determining the basis for a
taxonomy of mechanical ventilation. Respir Care 2012; 57 (4): 514-524.
10. Chatburn RL. Classification of
mechanical ventilators and modes of ventilation. In: Tobin MJ, ed. Principles
and practice of mechanical ventilation, 3rd edition. New York: McGraw-Hill, 2012.
11. Branson RD, Chatburn RL. Should
adaptive pressure control modes be utilized for virtually all patients
receiving mechanical ventilation? Respir Care 2007, 52(4):478-488.
12. Jaecklin
T, Morel DR, Rimensberger PC. Volume-targeted modes of modern neonatal ventilators: how stable is the
delivered tidal volume? Intensive care medicine 2007; 33 (2): 326-335.
13. Richey K. Adaptive Pressure Control:
tidal volume variance during simulated bariatric laparoscopic surgery. American
Society of Anesthesiologists 2009. Abstract presented at the annual meeting of
American Society of Anesthesiologists.
